1. Field of the Invention
The present invention pertains to a system, an apparatus, a program and a method for obtaining a time stamp, in order to update the time stamp.
2. Description of the Related Art
The time stamp is widespread to certify the existence of documents at each time. A time stamp providing apparatus that a so-called Time stamp Authority owns generates the time stamp. The time stamp providing apparatus generates the time stamp signing with a unique private key, to data that sets “Time” and “Hash value” of electronic data of the documents, etc. by using a technology of a digital signature. The time stamp certifies the existence of the electronic data corresponding to “Hash value” at the time by “Time” included in the time stamp.
Conventionally, in the case where it seemed the time stamp compromise by some reasons, a technology of extending validity term by newly generating a time stamp to the time stamp that already existed by other private keys is disclosed. (Refer to, for example, “GUIDELINE OF TIME STAMP FOR LONG-RUN GUARANTEE”, February, 2005, Time Business Forum (TBF), “URL:http://www.scat.or.jp/time/PDF/choukihosyouguidelin eVer1.1.pdf” searched on Jul. 15, 2005). Moreover, a technology that signed repeatedly according to the timing of the update of the private key is disclosed in Japanese patent Laid Open Publication (Kokai) No. 2002-6739.
However, according to the above technique disclosed in “GUIDELINE OF TIME STAMP FOR LONG-RUN GUARANTEE”, when it turned out back to have made the time stamp to compromise by point (time) at the past, the time stamp becomes invalid without giving the occasion for updating the time stamp. Therefore, there is a problem that the existence of the documents is not able to be certified.
Moreover, according to the above technique disclosed in Japanese patent Laid Open Publication (Kokai) No. 2002-6739, although there is a resistance to the falsification by making of the private key to compromise, it is not the time stamp. Therefore, there is a problem that the existence of the document at the time of the first signature is not able to be certified over a long period of time.